A typical one-way clutch used e.g. in a paper feeder of an office machine is disclosed in JP Patent publication 10-238560A (FIGS. 1 and 2), which includes an outer race rotatably mounted around a rotary shaft. A plurality of circumferentially spaced pockets are formed in the radially inner surface of the outer race. On the bottom of each pocket, a cam surface is formed which defines a wedge space having a predetermined wedge angle in cooperation with the outer periphery of the rotary shaft. In each pocket, a rolling element and a biasing spring biasing the rolling element toward the narrow end of the wedge space are received.
In this one-way clutch, when the rotary shaft rotates toward the narrow end of each wedge space, the rolling elements are wedged into the respective wedge spaces. The outer race and the rotary shaft are thus locked together and rotate together. When the rotary shaft rotates in the opposite direction, the rolling elements become disengaged from the respective wedge spaces, allowing the rotary shaft to rotate alone in the opposite direction.
This one-way clutch is used with the rotary shaft as an input and the outer race as an output. Conversely, the one-way clutch may be used with the outer race as an input and the rotary shaft as an output. If this one-way clutch is structured so that when the input member rotates in the forward direction, the clutch is locked, and in order to unlock the clutch, the rotary shaft has to be rotated in the reverse direction.
But according to the intended use, it may be necessary to unlock the clutch while the input member is rotating in the forward direction, thereby preventing transmission of rotation to the output member. On other occasions, it may be necessary to not only unlock the clutch but simultaneously rotate the output member in the reverse while the input member is rotating in the forward direction. The above-mentioned conventional one-way clutch, which can be unlocked only by rotating the rotary shaft, cannot meet these requirements. If larger maximum permissible torque is required for this type of conventional one-way clutch, it is necessary to increase the number of rolling elements and thus to correspondingly increase the outer diameter of the one-way clutch.
Use of an electromagnetic clutch would make it possible to prevent transmission of torque to the output member and simultaneously rotate the output member in the reverse direction while the input member is rotating in the forward direction. But an electromagnetic clutch further needs a commercial power source or a battery and corresponding wiring extending through the complicated device.